The present invention relates to a recording sheet conveyance apparatus used in an image recording apparatus or an image printing apparatus such as an electrophotographic copying apparatus.
Conventionally, the line speed of a photosensitive member and the feed speed of a copying sheet are determined independently of each other for a recording sheet conveyance apparatus of an electrophotographic copying apparatus. Thus, it is possible to increase the copying speed adequately, even by starting the feed of a new sheet from the feed sheet cassette at a high speed after the sheet is fed to the photosensitive member.
Such a conventional system, however, has encountered a problem such as the reduction of the sheet feeding speed where copying sheets of three different sizes have to be fed selectively, since the larger-sized copying sheet has a longer feed time than the smaller-sized copying sheet, thereby causing a reduction of the copying speed.
As a countermeasure against this problem, it has been devised to increase the conveyance speed and feed speed of the copying sheet or starting the feed of the next sheet from the feed sheet cassette before the feed of a sheet to the photosensitive member is completed. However, increasing the feed speed and conveyance speed of the copying sheet or starting the feed of next sheet from the feed sheet cassette before the feed of a sheet to the photosensitive member is completed is found to cause a new problem where the succeeding sheet runs into the preceding sheet from behind while the preceding sheet is waiting to be synchronized with the turn of the photosensitive member.
The present invention also relates to a feed sheet apparatus, especially a feed sheet apparatus for recording sheets constituting an independent unit from the copying apparatus.
In general, a feed sheet apparatus for feeding sheets to an apparatus such as a copying apparatus is incorporated in the copying apparatus.
More particularly, as seen from the general construction shown in FIGS. 39 and 40, a plurality of feed sheet cassettes 300 are disposed so that one contacts another, respectively, on the feed sheet side in the frame of the copying apparatus from the sheet feeding apparatus. The operation unit of the copying apparatus is first instructed of the stage from which the sheets are to be supplied, whereby the timer counter is set through sheet feeding sensor S1 for the conveyance of the sheets. The sheet feeding clutch is actuated to transmit the drive force of the sheet feeding motor, and only the setting of the timer needs to be done.
In the case of a conventional sheet feeding apparatus having the above-described mechanism, when the rear end of a sheet has left the sheet refeeding roller the succeeding sheet from the feed sheet cassette is sent to the waiting position of the sheet at a high speed by the sheet refeeding roller. In the case of the sheet feeding apparatus according to the present invention, however, the sheet is fed at a speed equal to or higher than the sheet feeding speed of the sheet refeeding roller.
When control of the speed in sending out the sheet carrier (including the control of the stop of the sheet) is lacking, there is the possibility that the succeeding sheet runs into the preceding sheet at the restart stage, in the sheet feeder which is changed freely with a sheet conveyance apparatus installed separately from the frame of the copying apparatus.
Further, the present invention relates to a sheet feeder which is separated from the copying apparatus and in which the sheet conveyance speed is made to coincide with the processing speed of the copying apparatus.
In general, for the sheet conveyance speed in the sheet feeder which is separated from the copying apparatus, the sheet feed speed is increased in feeding the sheet to the copying apparatus from the sheet feeder to let the sheet arrive at the sheet refeed roller, i.e., the resist roller of the copying apparatus, and then the speed is equalized to the speed of the image carrying member to form the desired image.
In the conventional system as described above, however, the sheet has to be sent to the copying apparatus at a high speed at each copying, so that, when the copying apparatus has to be operated at a high speed such as at 70 sheets/minute, the sheet conveyance path or sheet path becomes longer, and thus the copying apparatus is unable to fully exert its high-speed function, thereby causing the problem that the copying speed is governed by the sheet conveyance speed of the sheet feeder.
A further object of the present invention is to provide a sheet feeder which is free of this problem of the conventional system and enables high-speed copying by equalizing the sheet conveyance speed of the sheet feeder to the speed of revolution of the image carrying member so that the sheet can be allowed to be present even in the sheet conveyance path.